The term “transient characteristics of an engine” refers not to the steady state, in which the speed and torque remain constant, but to characteristics obtained in cases, in which they change with time. For instance, it refers to engine characteristics in states, in which the speed etc. changes, such as during acceleration or during deceleration.
The measurement of output characteristics of a conventional engine, such as the torque output, exhaust, etc., in the transient states of the engine has been conducted using a technique, in which an actual engine is brought into the steady state, the output state of the engine is subjected to measurement, and the output of the engine is then estimated by substitution with transient state characteristics obtained by weighting the steady-state output data.
However, the measurement of steady-state engine characteristics has been a time consuming procedure in which after making changes to the control value of a control factor (e.g. the quantity of injected fuel, fuel injection timing, etc.) of an engine one would wait until a predetermined time (e.g. 3 minutes) passes before the steady state is reached and then measure the output in this state, where one would make changes to the control value of one control factor, conduct measurements upon lapse of a predetermined time after reaching the steady state, and then again make changes to the control value of a control factor and conduct measurements, etc.
Incidentally, in an actual vehicle, during travel, the engine spends more time in a state of acceleration or deceleration and less time in a state permitting travel at a constant speed. For this reason, it is important to measure engine characteristics in transient states. In addition, in recent years, exhaust-related regulations have been directed not at regulation based on the steady-state exhaust values of an engine, as was done before, but at regulation based on regulatory values related to the transient-state exhaust of an engine. Consequently, it has become important to measure transient characteristics that define what kind of transient state exhaust is obtained when certain changes are made to certain control factors.
Incidentally, even during steady-state measurement, which was conducted, as described above, in order to determine what kind of output would be obtained if changes were made to the control factors of an engine in the steady-state, there were numerous control factors, with a particularly large number of control factors appearing when engine control was carried out by means of ECU-based electronic control, as a result of which the length of the test increased. For instance, parameters were added for various types of electronic control involved in engine control, such as EGR (Exhaust Gas Recirculation) valve control or VGT (Variable Geometry Turbo) control. During transient characteristics measurement, in a state in which the engine speed (rotational speed) and torque vary in the form of a time series, it is natural that the output data, likewise, appear as data varying in the form of a time series, as a result of which the number of control factors increases and the length of the test grows exponentially if measurements are attempted in the steady state by making changes to the control values of every single control factor.
For this reason, technology has been proposed, in which engine control etc. is evaluated using simulation virtually reproducing the characteristics of the engine and the vehicle (see Patent Document 1).
In this technology a virtual vehicle model, complete with an engine, is created for each vehicle type in a simulator in advance, whereupon various control inputs, for instance, control values for the throttle aperture, crank angle, and other control factors, are inputted into the vehicle model, and an attempt is made to estimate engine speed, vehicle speed, and exhaust temperature sensor values as outputs of the virtual vehicle model based on the inputted control values.
Because the number of control factors used in an engine has increased in recent years, when measurement of steady state and transient state characteristics is attempted in a real engine, as described above, it takes a long time to obtain test data, which has become a bottleneck in engine development.
In addition, the technique consisting in deploying a vehicle model, including a virtual engine model, in a simulator and using it to observe the behavior of the engine is useful in terms of allowing for reductions in the length of engine development. However, in the above-described Patent Document 1, the object is to build a simulation of a vehicle model and not to create a simulation of transient state phenomena in an engine and use it to evaluate required performance in the transient states of the engine. In addition, poor operability in making changes to the control values has been a problem in case of making changes to the control values of the respective control factors of an engine according to the transient state and estimating their results.